Feeding Interrelations Between Age-Groups of Pumpkinseed (Lepomis gibbosus) and Comparisons with Bluegill (L. macrochirus)

Abstract

Analysis of the stomachs of 2435 pumpkinseeds (Lepomis gibbosus) showed that the diet was made up largely of chironomid larvae, molluscs, isopods, with lesser quantities of amphipods, Trichoptera larvae, and Ephemeroptera nymphs. Cladocera were only important to the very young fish. Age-class separation, in terms of taxonomic and prey-size categories, was minor, although the diet changed somewhat with age. Quantification of the diet overlaps between year-classes (by Levins index) revealed overlap levels that were moderate to high, varying seasonally between 0.5 and 1.1. They were greatest in July when the diversity of available prey organisms fell and October when several size-classes simultaneously consumed isopods, then at a peak in biomass. The feeding and spatial ecology of the pumpkinseed was compared with that of a closely related congener, the bluegill (L. macrochirus). The two species and their equivalent year-classes separated out partially on diet (the bluegill consuming a greater proportion of Cladocera and Tnchoptera larvae; the pumpkinseed, molluscs and isopods), and partly on habitat and the height at which they foraged in the water column. Ecological overlap values between equivalent year-classes of the two species were moderate, 0.52–0.57 (Levins scale), on the basis of diet alone as well as when the habitat component was incorporated. It is suggested, however, that other differences serve to reduce these levels. Key words: feeding, year-class diets, sunfish, intraspecific competition, interspecific competition, prey invertebrates, Centrarchidae